A little under a year ago South Park introduced Captain Hindsight in episode "Coon 2: Hindsight." Like most one-off South Park characters, Matt Stone and Trey Parker created him to take aim at the ridiculousness of others, in this case mainstream media analysis after the Gulf oil spill.
I wasn't aware there was a meme until I saw this Reddit post this morning and it seems that Captain Hindsight has slowly gained mild traction on the web, and since everyone loves South Park and can identify with a super sucky aunt -- or annoying person in their life -- who loves to point out what they should have done, I think Captain Hindsight has WAY more potential than is currently being tapped. I'm pretty sure co-workers everywhere could create their own hilarious subculture based on the meme. I kind of wish I had a time machine so I could go back to my cubicle days and email a "If you didn't want lunch to suck donkey balls, you shouldn't have invited Steve" version to one of my friends in the office. Would have killed. Steve was the worst.
Anyhoo, here's the South Park clip followed by the best variations out there.